Polypropylene container and process for making the same

ABSTRACT

A multilayer plastic container comprises a layer of a polypropylene and an intermediate layer directly adjacent the layer of polypropylene wherein at least one of the polypropylene and intermediate layers comprises an adhesive such as maleic anhydride incorporated therein to adhere the layer of polypropylene to the layer of EVOH.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to oriented polymeric containers andprocesses for manufacturing the same; specifically, to orientedmultilayer containers having at least one layer of polypropylene (“PP”)and a layer of a barrier material providing a barrier to migration ofoxygen, carbon dioxide, fragrance or flavor.

2. Background

Many products desirable of being stored in plastic containers haverequired a barrier to control migration of carbon dioxide, oxygen,fragrance, flavor, etc. in order to maintain product freshness. Suchproducts included, by way of example only, certain carbonated beverages,fruit juices, beers, sauces, ketchups, jams, jellies and dry foods suchas instant coffees and spices. Most commercially acceptable transparentor semi-transparent containers that provided carbon dioxide and oxygenmigration control were constructed of at least one layer comprising apolyester such as polyethylene terephthalate (“PET”) and a barrier layercomprising ethylene vinyl alcohol copolymer (“EVOH”), nylon or otherknown barrier material. The polyester layer deterred migration ofmoisture, although poorly so when compared to other polymers such as PP,while the barrier layer provided an excellent barrier to migration ofcarbon dioxide, oxygen, etc.

When biaxially oriented, PET has long been known to be stronger and havelower haze values than PP. PET has also been known to provide a betterbarrier to oxygen and carbon dioxide migration than PP. Containers have,nonetheless long been constructed of PP because PP provided a betterbarrier to moisture migration than PET. For example, PP has been used toconstruct extrusion blow molded multilayer containers having one or morePP layers and a barrier layer to provide a PP container with oxygen orcarbon dioxide migration control. Such containers were only afforded themonoaxial orientation inherent in the extrusion blow molding process.Clarity of these bottles suffered accordingly. Monolayer biaxiallyoriented PP containers constructed by injection stretch blow molding orreheat stretch blow molding processes have also been employed to producelow haze oriented PP (“OPP”) structures.

Historically, PP has been significantly cheaper to purchase as a rawmaterial than has PET. PP has been known to better withstand the hightemperatures associated with hot-fill products than has PET. PP has beenknown to have a lower glass transition temperature, is semi-crystallineand crystallizes at a lower temperature than PET. Additionally, PP hasbeen known to have less built in strain than PET.

Beneficially, the melt temperature of most commercial grade PP has beenknown to be substantially lower than that of PET, bringing the PP melttemperature closer to that of EVOH. Unfortunately traditional PP did notreadily bond to most commercially feasible barrier materials. Failure tobond a barrier layer to an adjacent structural layer (such as of PET orPP) was made obvious to the naked eye due to reflection or refraction oflight and detracted from the clarity and aesthetics of a resultingstructure. Known PP containers with barrier protection thereforeemployed a discrete layer of an adhesive agent between a barrier layerand each adjacent PP layer to assure interlayer adhesion. This discretelayer of adhesive agent significantly reduced the clarity (i.e.increased the haze value) of the container. Moreover, known PPcontainers having a barrier layer were restricted to extrusion blowmolding and the mono-axial orientation afforded thereby. The mono-axialorientation afforded by extrusion blow molding left the PP withsignificantly higher haze values than its PET counterpart.

Having been burdened with the discrete layer of adhesive agent and beingafforded only the monoaxial orientation of extrusion blow molding, knownPP containers with barrier protection suffered from high haze values.Known PP containers with barrier protection have haze values ofapproximately 40-70%. Despite the advantages of PP, PET has, therefore,long been the material of choice for barrier containers when low hazewas desired.

SUMMARY OF THE INVENTION

The present invention comprises a method and apparatus for constructinga structurally sound PP container with barrier protection having a lowhaze value. The present invention also comprises a preform for reheatstretch blow molding a PP container with barrier protection and a lowhaze value. It is one objective of the present invention to provide acontainer having a layer comprised of PP and a layer comprised ofbarrier material adjacent to the PP layer wherein an adhesive isincorporated into at least one of the PP layer and the barrier layer forbonding the PP layer directly to the barrier layer.

It is an additional objective of the present invention to providemultilayer plastic containers having oxygen, carbon dioxide and moisturebarrier protection with a haze value of less than 25%.

It is another object of the present invention to provide containershaving a layer of enhanced PP and a layer of a barrier material directlyadjacent thereto.

It is another object of the present invention to provide containershaving a layer of a PP and a layer of enhanced barrier material directlyadjacent thereto.

It is another object of the present invention to provide a commerciallyacceptable, cost effective container with a low haze value having alayer comprising PP immediately adjacent to a layer comprising a barriermaterial.

It is still another object of the present invention to provide a barrierPP container having a haze value of less than 20%.

It is yet another object of the present invention to provide containersmeeting the above objects of the invention and having a high structuralintegrity.

It is an additional object of the present invention to provide barrierPP containers meeting the above objects of the invention and having thehigh structural integrity necessary to withstand hot-filling ofcommercial food products.

It is yet another object of the present invention to provide barrier PPcontainers meeting the above objects of the invention and having thehigh structural integrity necessary to withstand conventional methods ofsterilizing commercial food products.

It is a further object of the present invention to provide a preformhaving two different materials with similar melting temperatures tofacilitate more compatible injection molding of the preform.

It is yet an additional object of the present invention to provide abarrier PP container having a low haze value.

It is a still another object of the present invention to provide apreform for blow molding a barrier PP container.

It is still a further object of the present invention to provide apreform having a thickness profile designed to facilitate the blowmolding of a structurally sound barrier PP container.

It is a still another object of the present invention to provide apreform having a thickness profile designed to facilitate the blowmolding of a structurally sound barrier PP container having vacuumpanels, ribs or other structural reinforcing features.

It is an additional object of the present invention to provide a reheatprocess capable of heating a barrier PP preform to facilitate properbiaxial stretch blow molding of that preform into a commerciallyacceptable container.

It is still an additional object of the present invention to provide areheat process capable of efficiently heating a barrier PP preform to anapproximately uniform temperature to facilitate proper biaxial stretchblow molding of that preform into a commercially acceptable container.

It is yet another object of the present invention to provide a reheatprocess capable of efficiently heating a barrier PP preform to anapproximately uniform temperature without elevating any portion of thatpreform above its melt temperature.

It is still further object of the present invention to provide a processfor blow molding barrier PP containers on known blow molding equipment.

It is another object of the present invention to provide a process forblow molding barrier PP containers on blow molding equipment designedfor blow molding PET.

It is still another object of the present invention to provide a blowmolding stretchrod configured to be capable of high rates of heatconvection.

It is yet another object of the present invention to provide a widetipped blow molding stretchrod configured with fins, holes or otherelements increasing its surface area and, therefore, its capability ofhigh rates of heat convection.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of one container according to the presentinvention.

FIG. 2 is a perspective view of another container according to thepresent invention.

FIG. 3 is a perspective view of yet another container according to thepresent invention.

FIG. 4A is a perspective view of still another container according tothe present invention.

FIG. 4B is a perspective view of a further container according to thepresent invention.

FIG. 5 is a perspective view of still a further container according tothe present invention.

FIG. 6 is a vertical cross-sectional view of the container of FIG. 5taken through its longitudinal axis.

FIG. 7 is an out-take from the cross-sectional view of FIG. 6.

FIG. 8 is an out-take of a cross-section of an alternative wallconstructed according to the present invention.

FIG. 9 is an out-take of a cross-section of another alternative wallconstruction according to the present invention.

FIG. 10 is an out-take of a cross-section of yet another alternativewall construction according to the present invention.

FIG. 11 is a vertical cross-sectional view of a preform constructedaccording to the present invention, taken through its longitudinal axis.

FIG. 12A is a vertical cross-sectional view of another preformconstructed according to the present invention, taken through itslongitudinal axis.

FIG. 12B is a vertical cross-sectional view of yet another preformconstructed according to the present invention, taken through itslongitudinal axis.

FIG. 13A is an overlay of the preform cross-sectional view of FIG. 12Aonto the container cross-sectional view of FIG. 6.

FIG. 13B is an overlay of a cross-sectional view of a PET preformconstructed according to standard principals for stretch blow moldingthe container of FIG. 6 onto the container cross-sectional view of FIG.6.

FIG. 14 depicts a temperature-time diagram for heating a monolayer PPpreform according to the prior art.

FIG. 15 depicts a temperature-time diagram for heating a monolayer ormultilayer PP preform according to one embodiment of the presentinvention.

FIG. 16 depicts a top-side elevational view of a heating apparatus forheating a PP preform according to one embodiment of the presentinvention.

FIG. 17 depicts a cross-sectional view of the apparatus of FIG. 16.

FIG. 18 depicts an overhead view of another heating apparatus forheating a PP preform according to one embodiment of the presentinvention.

FIG. 19A-19D depict progressive stages of blow molding the preform ofFIG. 12A into the container of FIG. 6.

FIG. 20 depicts a prior art stretchrod deforming a blown container.

FIG. 21 depicts one embodiment of a stretchrod of the present invention.

FIG. 22A is a back-side elevational view of the tip of the stretchroddepicted in FIG. 21.

FIG. 22B is a cross-sectional view of the tip of the stretchrod depictedin FIG. 21.

DETAILED DESCRIPTION OF THE DRAWINGS

It has been found that the barrier PP container of the present inventioncan be achieved by reheat stretch blow molding a container from amultilayer preform comprising at least one layer of PP and at least onelayer of barrier material. The terms barrier, barrier material orbarrier layer shall mean the use of EVOH, nylon or other known polymericmaterial know to provide a barrier to migration of oxygen, carbondioxide, fragrance or flavor including, but not limited to, thosematerials having nano-composites or other non-polymeric materials knownto inhibit the migration of gases or materials known to absorb or“scavenge” gases such as oxygen. When generically referenced herein, PPshall mean any of PP homopolymers, random copolymers, block copolymersor random block polymers. A comonomer can be selected from the groupconsisting of ethylene, butylene, or other alpha-olefins from C₅-C₈. Apreferred comonomer is ethylene wherein the ethylene is up to 3.0 weight% of the polypropylene copolymer. The incorporation of nucleating agents(often referred to as “clarifiers” or “clarifying agents”) into the PPfor reducing the haze value, as known to those of ordinary skill in theart, is also contemplated. Clarifying agents are exemplified by MillikenChemical, Division of Milliken & Co.'s Millad 3988 clarifying agent orMitsui Toatsu Chemicals, Inc.'s NC4 clarifying agent. Other clarifierssuch as sorbitol and benzoates can also be used. Such clarifying agentsare typically present in the amount of 0.1-0.3% by weight of the PP.Commercially available materials that have been found to readilyfacilitate the present invention are discussed herein by way of exampleand are not intended to limit the scope of the invention.

FIG. 1 depicts one embodiment of a multilayer plastic container 10biaxially oriented according to the present invention. The container 10is depicted in the form a bottle having a narrow finish 12, a bodyportion 14 extending from the finish 12 to a base 16 with the body 14defining a cylindrical wall 20 and a shoulder 22. The cylindrical wall20 has an upper label protector 24 and a lower label protector 26 toprevent an adjacent container from damaging a label (not shown) on thecylindrical wall 20. The container 10 could be employed, for example, todeliver water, fruit juices or carbonated or other beverages. Variousother container configurations, such as those discussed below, are alsosusceptible of construction according to the present invention.

FIG. 2 depicts another container embodiment 28 according to the presentinvention. The container 28 has a wide-mouth finish 30, a body portion32 extending from the finish 30 to a base 34 with the body 32 defining acylindrical wall 36 and a shoulder 38. The cylindrical wall 36 has anupper label protector 40 and a lower label protector 42. The container28 is depicted in the form of a wide-mouth bottle having vacuum panels44, often referred to as windows, to strengthen the cylindrical wall 44against buckle due to low pressure in the container 28 resulting fromprocesses such as hot-filling or warm-filling, as will be understood byone of ordinary skill in the art, typical of filling processes employedfor fruit juices. The windows 44, or other known support features, maybe of any known configuration. The configuration of container 28 is morefully disclosed in U.S. Pat. No. D445,693S, the entirety of which isincorporated herein by reference.

FIG. 3 depicts yet another container embodiment 46 according to thepresent invention. The container 46 is representative of a typicalwide-mouth jar configuration. The container 46 has a wide-mouth finish48, a body portion 50 extending from the finish 48 to a base 52 with thebody 50 defining a cylindrical wall 54 and a shoulder 56. Thecylindrical wall 54 has an upper label protector 58 and a lower labelprotector 60. The container 46 is depicted in the form of a wide-mouthjar typically employed for products such a jams and jellies, red saucesand dry goods such as ground coffees.

The containers of FIGS. 4A, 4B and 5 depict container configurationssimilar to that of the container 46 depicted in FIG. 3 with the additionof support features to reinforce the respective sidewalls against buckleunder vacuum. FIG. 4A depicts a container embodiment 62 having awide-mouth finish 64, a body portion 66 extending from the finish 64 toa base 68 with the body 66 defining a cylindrical wall 70 and a shoulder72. The cylindrical wall 70 has an upper label protector 74 and a lowerlabel protector 76. The container 62 is depicted in the form of awide-mouth jar having vacuum panels 78. The vacuum panels 78, or otherknown support features, may be of any known configurations. Theconfiguration of container 62 is more fully disclosed in U.S. Pat. No.D445,339S, the entirety of which is incorporated herein by reference.FIG. 4B depicts a container embodiment 80 having a wide-mouth finish 82,a body portion 84 extending from the finish 82 to a base 86 with thebody 84 defining a cylindrical wall 88 and a shoulder 90. Thecylindrical wall 88 has an upper label protector 92 and a lower labelprotector 94. The container 80 of FIG. 4B is depicted in the form of awide-mouth jar having vacuum panels 96 similar to vacuum panels 78 ofthe container depicted in FIG. 4A, with the addition of islands 98 tofurther strengthen the cylindrical wall 88, as known in the art, as wellas provide support for a label (not shown) placed on the cylindricalwall 88. The vacuum panels 96 and islands 98, or other known supportfeatures, may be of any known configurations.

FIG. 5 depicts a container embodiment 100 having a wide-mouth finish102, a body portion 104 extending from the finish 102 to a base 106 withthe body 104 defining a cylindrical wall 108 and a shoulder 110. Thecylindrical wall 108 has an upper label protector 112 and a lower labelprotector 114. The container 100 is depicted in the form of a wide-mouthjar having annular ribs 116 to strengthen the cylindrical wall 108, asknown in the art. The annular ribs 116, may be of any number or knownconfigurations. The configuration of container 100 is more fullydisclosed in U.S. patent application Ser. No. 29/119,063, the entiretyof which is incorporated herein by reference.

The containers depicted in FIGS. 1-5 each represent an alternative tocontainers of like configurations constructed of PET and may optionallybe provided with barrier protection from one or more barrier layers. Thecontainer configurations contemplated as susceptible of beingconstructed from OPP according to the present invention are limitlessand the scope of the invention is not limited to those containerconfigurations depicted herein. Rather, the containers of FIGS. 1-5 aredepicted to indicate the broad range of capabilities that can beachieved with containers constructed according to the present invention.For example, despite all of the containers depicted, and describedherein, being of cylindrical configuration, non-cylindrical containersmay also be constructed according to the present invention and the sameprincipals discussed herein in relation to the construction ofcylindrical containers also apply to non-cylindrical containers.

Barrier PET containers have become the industry standard formanufacturers of oxygen sensitive consumer goods who wish to providetheir products in transparent or semi-transparent (collectivelyreferenced herein as “low haze”) barrier containers. The barrier OPPcontainers of the present invention provide a relatively inexpensivealternative to barrier PET. Due in part to the stability of PP atrelatively high temperatures, as compared to PET, the containers of thepresent invention are ideally suited for high heat processing such asfor purposes of sterilization. For example, as discussed above, thepresent invention has been found to produce containers capable ofwithstanding hot-filling at standard parameters. It is also contemplatedthat containers manufactured according to the present invention are wellsuited for other methods known in the art for sterilizing consumerproducts, such as, by way of example, pasteurization and retort.

The advantages of the present invention also extend to consumer goodsnot requiring heat treatment. For example, injection of the multilayerpreforms of the present invention is simplified over injection of theirPET counterpart, because the injection temperature of PP (typicallyranging from approximately 200-220° C.) is close to that of EVOH(typically ranging from approximately 190-210° C.), the barrier materialof one embodiment of the invention. Therefore, the injection equipmentemployed to construct preforms according to the present invention neednot be designed to maintain a significant temperature differentialbetween those melt materials. Moreover, all containers of the presentinvention will benefit from the relatively low cost of PP as compared toPET while achieving comparable haze values and overall aesthetics.

Interlayer Construction

FIG. 6 depicts a cross-sectional view of the container 100 depicted inFIG. 5. The various wall constructions set forth below can apply equallywell to other container configurations contemplated by the presentinvention, whether or not depicted herein. Moreover, it is contemplatedthat the present invention may apply to all multilayer PP containers,with or without a barrier layer. Accordingly, the terms “intermediatelayer” will be used herein to generically refer to a layer positionedintermediate of two PP layers in a preform or container and may,although it need not, comprise a barrier layer. It is also contemplatedthat each preform or container configuration described or shown hereinmay be supplied with a non-barrier intermediate layer in the place ofthe barrier layer discussed.

As depicted in FIG. 6, a barrier layer 118 extends throughout the bodyportion 104 and into both the finish 102 and the base 106. For theclarity of FIG. 6, the barrier layer 118 is represented by a single linerather than depicted with a thickness having cross-hatching. Therespective barrier layers of FIGS. 11, 12A-B, 13A-B, 17, 19A-D, 20 and21 are likewise represented by a single line. The barrier layer 118,where present, divides the container 100 into an inner layer 120 and anouter layer 122. FIG. 7 depicts an out-take of the wall 108 to providean enhanced view of the multi-layer structure. The inner layer 120 andthe outer layer 122 are each preferably comprised of the same materialcomposition to simplify the equipment necessary for injecting preformsfrom which the container 100 is blown. It is contemplated, however, thatthe material compositions of the inner and outer layers 120 and 122could differ one from the other such as, by way of example only,incorporating a clarifying agent into only the outer layer 122.

The inner and outer layers 120 and 122 comprise at least PP and providea majority of the thickness and structural rigidity to the bottle 100,and, as such, may be referenced herein as “structural layers.” Thebarrier layer 118 is comprised of at least a barrier material or asdiscussed generally above and more specifically below. The materialcompositions of the layers 118, 120 and 122 facilitate adhesion, bondingor tying between each of the structural layers 120 and 122 and thebarrier layer 118 to prevent delamination of the container 100 undernormal conditions. Reference herein to any one of the terms “adhesion,”“bonding” or “tying” may, alternatively, represent reference to any ofthe others where not inconsistent.

In one embodiment, the polymer structure of either the PP or the barriermaterial is modified from known compositions to facilitate adhesionbetween the two materials in a process often referred to as“compatiblizing” one polymer with the other. In an alternativeembodiment, an adhesive is incorporated into the material of at leastone of the barrier layer 118 and the structural layers 120 and 122. Forexample, the structural layers 120 and 122 may comprise a PP with anadhesive incorporated therein while the barrier layer 118 is comprisedof a pure barrier material. Alternatively, the structural layers 120 and122 may comprise pure PP while the barrier layer 118 is comprised of abarrier material with an adhesive incorporated therein. In yet anotheralternative embodiment, each of the layers 118, 120 and 122 couldincorporate an adhesive to facilitate adhesion therebetween. A PP thathas been compatiblized or made to incorporate an adhesive will bereferred to herein as “enhanced PP” or an “enhanced PP layer.” A barriermaterial that has been compatiblized or made to incorporate an adhesivewill be referred to herein as an “enhanced barrier material,” “enhancedbarrier layer,” or “enhanced EVOH” or “enhanced nylon” when materialspecific.

One embodiment of an “enhanced PP” comprises blending, for example bydry blending, Tymor 2E02 adhesive agent (manufactured by Rohm and Haas)into Solvay KB 4285 PP (referenced herein as “Solvay 4285”) as a base PPto disperse the Tymor 2E02 throughout the base PP as evenly as possible.Tymor 2E02 comprises a PP functionalized with a maleic anhydride in theamount of approximately 0.2% by weight. Tymor 2E02 is dispersedthroughout the base PP in the amount of up to approximately 15% byweight to provide the enhanced PP with up to approximately 0.03% byweight of maleic anhydride. The Tymor 2E02 PP onto which maleicanhydride is grated, can be any known PP. However, when used inconcentrations over approximately 10% by weight, it is preferred,although not necessary, that the Tymor 2E02 comprise the same PP as thebase PP into which it is to be incorporated.

Another embodiment of an “enhanced PP” comprises blending, for exampleby dry blending, Tymor 2E04 adhesive agent (manufactured by Rohm andHaas) into Solvay 4285 PP as a base PP to disperse the Tymor 2E04throughout the base PP as evenly as possible. The Tymor 2E04 comprises aPP functionalized with a maleic anhydride in the amount of approximately0.8% by weight. The Tymor 2E04 is dispersed throughout this base PP inthe amount of up to approximately 15% by weight to provide the enhancedPP with up to approximately 0.12% by weight of maleic anhydride. As withthe Tymor 2E02, the Tymor 2E04 PP onto which the maleic anhydride isgrafted can be any known PP. However, when used in concentrations overapproximately 10% by weight, it is preferred, although not necessary,that the Tymor 2E04 comprise the same PP as the base PP into which it isto be incorporated.

A further embodiment of an “enhanced PP” comprises blending, for exampleby dry blending, Fusabond 353D (manufactured by DuPont) adhesive agentinto Solvay 4285 PP as a base PP to disperse the Fusabond 353Dthroughout the base PP as evenly as possible. The Fusabond 353Dcomprises a PP functionalized with a maleic anhydride in the amount ofapproximately 1.0% by weight. The Fusabond 353D is dispersed throughoutthis base PP in the amount of up to approximately 5% by weight toprovide the enhanced PP with up to approximately 0.05% by weight ofmaleic anhydride. The Fusabond 353D base PP can be any known PP.

The invention also contemplates the incorporation of alternativeadhesives agents into a base PP. For example, the following adhesiveagents have been found to provide acceptable adhesion between a base PPand a barrier material when employed to create an enhanced PP: Fusabond411D and Fusabond 536D (both manufactured by DuPont); and Tymor 2E07(manufactured by Rohm and Haas). The identified adhesive agents are notintended to represent an exhaustive list of possible adhesive agents andothers not mentioned here are contemplated.

Although any barrier material may be employed in a barrier layer of thepresent invention several barrier materials have been found to readilyadhere to an adjacent enhanced PP layer, especially when the PP isenhanced with one of the above-identified adhesive agents. These barriermaterials are: F-104BW EVOH, XEP-561 EVOH, XEP-719 EVOH, XEP-721 EVOHand ETC-127 EVOH (all manufactured by Evalca); Soarus D2908 EVOH andSoarus SG430 EVOH (all manufactured by Soarus); Grivory G21 nylon(manufactured by EMS-Chemie); and type 6001 MxD6 nylon (manufactured byMitsubishi Gas Chemical). These agents are listed by way of example onlyand other barrier materials are contemplated.

One embodiment of an “enhanced barrier layer” comprises blending, suchas by dry blending, Tymor 2E02 adhesive agent into F-104BW EVOH as abase barrier material to disperse the Tymor 2E02 throughout the basebarrier material as evenly as possible. As set out above, the Tymor 2E02comprises maleic anhydride in the amount of approximately 0.2% byweight. The Tymor 2E02 is dispersed throughout this base barriermaterial in the amount of up to approximately 15% by weight to providethe base barrier material with up to approximately 0.03% by weight ofmaleic anhydride.

In one embodiment, adhesive agents that require a smaller concentrationof the adhesive agent within the base barrier material are preferredadhesive agents for an enhanced barrier layer. The adhesive agentsthemselves typically being poor barriers to oxygen, carbon dioxide,etc., it is believed that the adhesive agent, when integrated into thebarrier material, deteriorates the barrier capabilities of the barriermaterial by reducing the thickness of the barrier material, or eveneffectively poking holes in the barrier layer, wherever chains of theadhesive agent are located in the barrier layer. By way of example, theTymor 2E04 has a higher concentration of maleic anhydride than the otherlisted adhesive agents and it requires less non-barrier material in thebarrier layer than, for example, Tymor 2E02 to provide the same amountof maleic anhydride.

As used herein to describe the incorporation of a commercial adhesiveagent such as Tymor 2E02 into a base material such as Solvay 4285 PP,the term “dry blending” refers to dispersing pellets of each into theextruder of the injection apparatus to be melted together as they areadvanced through the extruder. Blending in this manner results in chainsof the commercial adhesive agent entangled in the chains of the base PPas will be understood by those of ordinary skill in the art. When theadhesive agent comprises maleic anhydride grafted onto PP, the adhesiveagent may also be referred to as maleated PP. Blending in this mannermay also be employed to incorporate an adhesive agent into a basebarrier material. Other methods of incorporating an adhesive agent intoa base material (be it PP or barrier material) are contemplated and willbe evident to one of ordinary skill in the art.

In one embodiment of the present invention, the concentration of theadhesive agent within each of the structural layers 120 and 122 coulddecrease from a higher concentration at the extremity of each respectivelayer immediately adjacent to the barrier layer 118, to a lower (orzero) concentration at the extremity of the layer opposite the barrierlayer 118.

It has been found that the greater the percentage of adhesive agentevenly distributed throughout any layer of the container 100, the betterthat layer will adhere to an adjacent layer. This correlation resultsfrom two facts. First, the adhesive force that an enhanced layer mayexert on an adjacent layer of a container depends, at least in part,upon the amount of adhesive agent available at the outer surface of thatenhanced layer to interact (i.e. adhere, bond or tie) with the adjacentlayer. Second, as the percentage of adhesive agent evenly distributedthroughout any layer is increased, the amount of adhesive agent whichwill be exposed at an outer surface of that layer will also necessarilyincrease. Additionally, the percentage of the adhesive agent in a layerwhich is exposed at the outer surface thereof, is inversely proportionalto the thickness of that layer. That is, a thinner enhanced layer willproduce greater adhesive potential from a given quantity of an adhesiveagent, than will a relatively thicker enhanced layer comprised of thesame given quantity of adhesive agent. From the foregoing it will beunderstood that because the barrier layer 118 of the container 100 isthinner than each of the inner and outer layers 120 and 122, dispersingan adhesive agent in the barrier layer 118 will necessarily decrease theamount of adhesive agent necessary to bond the inner and outer layers120 and 122 to the barrier layer 118 relative to the dispersing theadhesive agent within the inner and outer layers 120 and 122.

Returning to the embodiment of FIG. 6, the barrier layer 118 terminatesat a finish end 124 short of an uppermost extremity 126 of the finish102 leaving a ring 128 of enhanced PP about the uppermost extremity 126of the finish 102. As is known to one of ordinary skill in the packagingart, extending the barrier 118 to the uppermost extremity 126 of thecontainer finish 102 would completely detach the inner layer 120 fromthe outer layer 122 and allow rather easy separation of the inner andouter layers 120 and 122. Separation of the inner and outer layers 120and 122 from the barrier layer 118 at the finish 102 would become likelybecause only the adhesive agent would be left to maintain the structurallayers 120 and 122 laminated to the barrier 118. Delamination at thefinish 102 would provide an aesthetically unpleasing container andexpose the barrier layer 118 to moisture which, in the case of EVOH forexample, dramatically reduces the barrier layer resistance to migrationof oxygen. Moreover, if the container were intended to facilitate humanconsumption directly from the container, separation of the layers at theupper extremity of the finish could result in injury to a consumer. Thebarrier layer 118 also terminates at a base end 130 short of theinjection gate area at the center 132 of the base 106 leaving a disc 134of enhanced PP about the base center 132. As will be understood by oneof ordinary skill in the art, the disc 134 pins the structural layers120 and 122 one to the other and helps to prevent delamination frominitiating in the base 106. However, a barrier layer extendingcontinuously across the entire base 106 is also contemplated by thepresent invention.

While it is desirable to locate the barrier layer 118 short of thefinish uppermost extremity 126 and the base center 132 to preventdelamination, the portions of the container left absent of barriermaterial are subject to relatively undeterred oxygen migration due tothe low oxygen barrier properties of known PP. Accordingly, it isdesirable to place the barrier layer finish end 124 close to the finishuppermost extremity 126 and the barrier layer base end 130 close to thebase center 132 to assist in maintaining lamination without creating anunnecessarily large area of the container through which oxygen willreadily migrate. It has been found that placing the barrier finish end124 within 0.100 inches (0.254 cm) from the finish uppermost extremity126 meets the described goals. As understood by those of ordinary skillin the art, placement of the barrier layer ends 126 and 130 is dictatedand controlled by the specific parameters employed in the process ofinjecting the preform from which the resulting container is blow molded.By way of example only, the barrier layer finish end 124 can be broughtwithin a few mils of the finish uppermost extremity 126 by creating abarrier fold-over during injection as described in U.S. Pat. No.4,554,190, the entirety of which is incorporated herein by reference.Other injection techniques to accomplish the discussed barrier placementwill become evident to one of ordinary skill in the art.

The PP of the inner and outer layers 120 and 122 provide structuralrigidity and moisture barrier protection to the container 100. Thethickness of the inner and outer layers 120 and 122 and the thickness ofthe barrier layer 118 are designed according to factors such as the typeof product to be filled in the container, the sensitivity of the productto oxygen, the desired shelf life of the product and whether or not thecontainer will be hot-filled or subjected to other sterilizationprocesses such as retort, etc. Typically the thickness of the inner andouter layers 120 and 122 are in the range of between approximately0.005-0.015 inches (0.0127-0.0381 cm) each for typical consumer goodsapplications and the barrier layer thickness is typically betweenapproximately 0.0001-0.002 inches (0.000254-0.00508 cm) for suchapplications. However, these thicknesses may be modified to vary, forexample, the container's rigidity, moisture barrier and/or oxygen andcarbon dioxide barrier as will be recognized by one of ordinary skill inthe art. Layer thicknesses are discussed further below with specificexamples in reference to FIG. 13A.

The present invention is not limited to the three layer wall structuresdescribed hereinabove. Accomplishing adhesion between two adjacentlayers by incorporating an adhesive agent into at least one of thoselayers may be applied to other wall structures as well. For example, atwo layer container (not depicted) is contemplated as having aninnermost layer of PP adhered to an outer layer of barrier materialwherein either the PP or the barrier material is enhanced, according tothe present invention, with an adhesive agent. This structure isbeneficial when employing a barrier material that is not as sensitive tomoisture as some barrier materials, such as EVOH, and is resistant toflaking or chipping when subjected to the normal rigors of a consumergood container.

Alternatively, another two layer container (not depicted) iscontemplated as having an innermost layer of barrier material and anouter layer of PP wherein either the barrier material or the PP isenhanced, according to the present invention, with an adhesive agent.This structure is beneficial for packaging consumer products, such as,by way of example only, orange juice that tend to have certain flavorcomponents absorbed by many PP compositions, because the barriermaterial can act as a barrier to the migration of the flavor component.Conversely, the innermost barrier layer can act as a barrier to themigration of components of the PP layer, or an adhesive agent therein,into the packaged product.

Adhering two adjacent layers one to the other according to the presentinvention can also be applied to more complicated structures includingthose constructed by extrusion blow molding techniques such as thosedescribed in U.S. Pat. No. 5,156,857, the entirety of which isincorporated herein by reference. For example, FIG. 8 depicts an outtakefrom the wall of six-layer container (container not depicted) comprisingan innermost layer of barrier material 136 immediately adjacent to aninner layer of PP 138 which is, in turn, immediately adjacent to anintermediate layer 140 of barrier material. The intermediate layer 140of barrier material is adhered by a discrete adhesive layer 142 to aregrind layer 144. An outermost layer of virgin PP 146 covers theregrind layer 144. The outermost layer 146 and the regrind layer 144adhere to one another without the assistance of an adhesive agent aswill be recognized by one of ordinary skill in the art. Discreteadhesive layer 142 is a traditional layer of adhesive, such as pureTymor 2E02, as is known in the art. The inner layer of PP 138 betweenthe innermost layer of barrier material 136 and the intermediate layer140 of barrier material comprises an enhanced PP to provide laminationto the two adjacent barrier layers 136 and 140. The inclusion of regrindlayer 144 renders this embodiment of the invention ripe for manufactureby standard extrusion blow molding processes known to those of ordinaryskill in the art. FIG. 9 depicts another wall construction of thepresent invention which comprises the wall construction depicted in FIG.8 without the regrind layer 144. The wall construction of FIG. 9 lendsitself to reheat stretch blow molding which creates no scrap and,therefore, has no need for the regrind layer 144.

FIG. 10 depicts an alternative to the wall construction depicted in FIG.8 wherein the discrete adhesive layer 142 has been eliminated. In thisembodiment, the regrind layer 144 is also an enhanced layer tofacilitate adhesion to the barrier layer 140. As with the embodimentdepicted in FIG. 8, the regrind layer 144 could be eliminated from thestructure in an alternative embodiment intended for manufacture by thereheat stretch blow molding method. In this alternative embodiment (notdepicted), the outermost layer 146 is an enhanced layer in order tofacilitate adhesion between itself and the adjacent intermediate barrierlayer 140. Other alternative configurations will become apparent tothose of ordinary skill in the art and are also contemplated by thepresent invention.

Preform

As with any preform designed for reheat stretch blow molding, thepreforms of the present invention are designed to allow for efficientreheating and blow molding to provide a container having a materialdistribution that will be capable of withstanding the rigors to which itwill be subjected. Primary among the concerns of designing a preform arethe material distribution and orientation in the resulting container.Orientation of the preform material is achieved by raising the preformto a blow temperature below the melt temperature, axially elongating thepreform with a stretchrod and expanding the preform radially to conformthe preform to the mold cavity in which the preform resides. Optimumorientation can be achieved at a range of blow temperatures. As will beunderstood by one of ordinary skill in the art, all portions of thepreform that will be expanded during blow molding must be within therange of blow temperatures during blow molding in order to obtain thedesired material distribution and in order to orient those portions ofthe preform.

Thermal conductivity of PP is substantially lower than that of PET. Forexample, the thermal conductivity of PP has been found to beapproximately 3.58 (10⁻⁴ cal)/(cm sec. ° C.). PET, on the other hand hasbeen found to have a thermal conductivity of approximately 6.92 (10⁻⁴cal)/(cm sec. ° C.). Similarly, PP has a higher heat capacity than PETcausing it to hold heat longer than PET. For example, the heat capacityof PP has been found to be approximately 0.53 cal/g° C. whereas PET hasbeen found to have a heat capacity of approximately 0.32 cal/g° C.Because of the differences in thermal conductivity and capacitance, a PPpreform will take substantially longer than a like configured PETpreform to heat from a given ambient temperature to an approximatelyuniform given blow temperature, as will be recognized by one of ordinaryskill in the art. The PP preform also takes longer than the likeconfigured PET preform to cool from a given injection temperature to agiven ambient temperature. Blown containers of PP face a longer cooltime as well.

The combination of the low thermal conductivity, high heat capacitanceand high blow molding temperatures of PP dictate increased reheat timesfor PP preforms over like configured PET preforms. The preformconfiguration of the present invention overcomes the differences inthermal conduction and capacitance between PP and PET to allow efficientreheating for blow molding.

The range of temperatures in which PP will orient during blow molding issubstantially narrow in comparison to that of PET. In one embodiment ofthe present invention, that temperature range (sometimes referencedherein as a “blow process window”) has been found to be approximately125-135° C., more preferably 128-132° C., for PP whereas a typical PETblow process windows ranges from 95-110° C. Blow process windows forother PP grades are contemplated and will be recognized by one ofordinary skill in the art or determined through routine experimentation.It has been found that the entirety of those portions of the preform tobe expanded during blow molding must be brought within the blow processwindow in order to properly blow mold an OPP container. If the outerskin of the preform is elevated to a temperature within the blow processwindow, 132° C. for example, but the inner skin is at a temperatureoutside the blow process window, 120° C. for example, with a temperaturegradient therebetween, at least those portions of the preform not withinthe blow process window will not properly orient and will cause adefective container. In extreme cases, blowing a preform having innerportions below the blow process window can result in preventing properinflation of the preform. If the outer skin is raised above the blowprocess window, insufficient orientation will be induced to produce anacceptably rigid container. Alternatively, if outer portions of thepreform are blown at temperatures above the blow process window, thestrain hardening necessary to cause the preform to inflate, as opposedto simply tearing under the blow pressure or stretchrod force, may beinsufficient to hold the preform together during inflation. In such acase, one or more holes will open in the preform allowing the blowpressure to escape from within the preform preventing formation of acontainer.

Moreover, the degree of strain hardening will vary with the blowtemperature, even within the blow process window, and “placement,”during blow molding, of the various portions of the preform incorresponding portions of the mold cavity will vary with the blowtemperature. For example, insufficient strain hardening, resulting froma high blow temperature, will allow portions of the preform to elongatemore than designed and redistribute the preform portions lower in theresulting container than designed, as will be recognized by one ofordinary skill in the art. For example, the lower portions of thepreform sidewall will be deposited in the base of the blow mold suchthat the base of the resulting container will comprise the material fromthe preform base portion as well as portions of the preform sidewall.The material in the base will not be able to stretch enough tosufficiently orient the base material, resulting in a defectively weakcontainer base. The excess elongation of the preform will also producethinner walls than desired. It will be understood by one of ordinaryskill in the art that blowing a preform having portions at temperaturesbelow the blow process window may result in upwardly redistributingportions of the preform and ultimately over thinning the base of theresulting container.

Straying from the blow process window can also result in delaminatingmultilayer preforms. The various layers of a multilayer preform, such asthose containers of the present invention having a barrier layer, may becaused to separate due to variation in the degree of resistance toinflation, as will be recognized by one of ordinary skill in the art.

To avoid the various problems that can result from blowing preformshaving portions thereof at temperatures outside of the blow processwindow, one embodiment of the preform of the present invention compriseswalls that are substantially thinner than walls in known PET preformdesigns for construction the same container. As discussed in more detailbelow, thinning the preform walls reduces the temperature differentialbetween the inner skin and the outer skin that will result duringreheating and facilitate a more uniform temperature making it easier tomaintain the entirety of the preform within the blow process window.Also, the time necessary to elevate the preform to the desiredtemperature is decreased. In one embodiment, the preform wall isdesigned to facilitate raising the entire preform wall to a temperaturein the range of 128-132° C. during a commercially acceptable period ofreheating. While the preform walls are ideally brought to a uniformtemperature, one of ordinary skill in the art will recognize that thetime required to bring a PP preform to a uniform temperature iscommercially unattractive with current reheat processes and preformdesigns.

While each of the preforms depicted herein are multilayer, the preformdesigns, including thickness profiles, set out herein apply equally tomonolayer preforms. FIG. 11 depicts one preform configuration of thepresent invention constituting a narrow-mouth elongated preform 148 ofthe type employed for reheat stretch blow molding elongated bottles suchas the bottle 10 depicted in FIG. 1 herein. The preform 148 comprises aninner layer 150, an outer layer 152 and a barrier layer 154. The preform148 is configured to define a finish 156, a neck 158 extending from thefinish 156 and a body portion 160 extending from the neck 158 to a base162 with the body defining a cylindrical wall portion 164 and a shoulderportion 166 between the neck 158 and the cylindrical wall portion 164.The neck 158 and body portion 160 defining a blow portion that will beexpanded during blow molding.

FIG. 12A depicts a wide-mouth preform 168 of the type employed forreheat stretch blow molding a container such as any of those of the typedepicted in FIGS. 3, 4A, 4B and 5 herein. The preform 168 comprises aninner layer 170, an outer layer 172 and a barrier layer 174. The preform168 is configured to define a finish 176, a body portion 178 and a base180 with the body 178 defining a cylindrical wall portion 182 and ashoulder portion 184. A neck portion 186 extends between the shoulder178 and the finish 176. The neck 186, body portion 178 and base 180define a blow portion that will be expanded and stretched during blowmolding.

FIG. 12B depicts an alternative wide-mouth preform 188 of the typeemployed for reheat stretch blow molding a wide-mouth container such asany of those of the type depicted in FIGS. 3, 4A, 4B and 5 herein. Thepreform 188 comprises an inner layer 190, an outer layer 192 and abarrier layer 194. The preform 188 is configured to define a finish 196,a body portion 198 and a base 200 with the body 198 defining acylindrical wall portion 202 and a shoulder portion 204. A neck portion206 extends between the shoulder 204 and the finish 196. The neck 206,body portion 198 and base 200 defining a blow portion that will beexpanded and stretched during blow molding.

Returning to FIG. 12A, the blow portion of the preform 168 of thepresent invention defines a wall thickness profile, described below butnot depicted, designed to facilitate both an efficient reheating and adesired thickness profile in the resulting container. The neck 186extends from the finish 176 at a relatively thin wall thickness t1. Inone embodiment, the wall thickness of the preform 168 graduallyincreases from thickness t1 along the neck and body portion 178 untilreaching the thickness t2 at the interface with the base portion 180.The base portion 180 extends until the base thickness again reaches thethickness t2 proximate a centerline 208 of the preform 168 to define awall portion of increased thickness 187 in the base 180. The preformwall thickness then begins to thin from thickness t2 until reaching athickness t3 at the preform centerline 208. While the thickness t3 ispreferably thinner than wall thickness t2, it is contemplated that thethickness t3 may equal or exceed thickness t2. The thickness of the wallportion of increased thickness 187 can vary from thickness t2 betweenits ends to accomplish the purposes discussed below. Alternatively, asdepicted in FIG. 12A, the wall portion of increased thickness 187 mayhave an approximately constant thickness t2 throughout.

The blow portion of the preform 168 has an overall height a, a baseportion 180 height b, and a height c at the lower end of the wallportion of increased thickness 187. In one embodiment, the barrier layeris run roughly along a preform wall centerline (not shown) between theinner and outer skin of the preform 168 dividing the inner and outerlayers 170 and 172 into approximately even thicknesses at any givenpoint on the preform 168. It is, however, recognized that the barrierlayer 174 may be moved closer to the inner or outer skin from the wallcenterline. In the preform 168 depicted in FIG. 12A, a barrier layer 174of approximately between 0.008-0.010 inches (0.02032-0.0254 cm)throughout the preform has been found to provide a sufficient barrierwhen the preform 168 is comprised of the below specified thickness forblow molding into a resulting OPP container of the configuration anddimensions of the container 100. Other barrier thickness arecontemplated to increase or decrease the resistance to migration ofgases, etc. in the container 100 and one of ordinary skill in the artwill recognized the variations necessary in the preform 168 toaccomplish variations in the resulting container 100.

The thickness profile discussed above in relation to FIG. 12A has beenfound to induce sufficient orientation in the preform 168, when thestructural layers 170 and 172 are comprised of PP, to facilitate blowmolding of high quality rigid container 100 as depicted in FIG. 13A. Aswill be recognized by one of ordinary skill in the art, the relativethicknesses of the preforms to the containers shown in the variousfigures, and most evidently in FIGS. 13A,B and 19A-D, have not beenmaintained in proper proportion so that a discernable cross-section ofthe container walls may be maintained. It is believed that therelatively thin neck portion 186 facilitates a thin, but orientedcontainer neck portion. Because little axial or radial stretching isimparted to the neck portion of a typical container, the neck portion186 is configured to be relatively close to the desired container neckthickness. The wall portion of increased thickness 187 provides areserve of material to be placed in the base of the correspondingcontainer during blow molding to provide the base with the materialnecessary for strength and drop impact resistance. Other preformthickness profiles and contours are contemplated and will become evidentto those of ordinary skill in the art.

FIG. 13A depicts an overlay of the preform 168 depicted in FIG. 12A ontothe container 100 depicted in FIG. 6 to demonstrate one embodiment ofthe correlation between the portions of a preform of the presentinvention and a container blow molded therefrom. As depicted, the neckportion 186 of the preform 168 is blown into a neck portion 210 of thecontainer 100, the shoulder portion 186 of the preform 168 is blown intoa shoulder portion 212, the cylindrical wall portion 182 is blown intothe cylindrical wall 214, the wall portion of increased thickness 187 ofthe preform base 180 is blown into an outer portion 216 of the containerbase 218 as well as the contact ring which contacts the surface on whichthe container 100 rests. The relative size of the preform 168 to thecontainer 100 as well as the thickness profile of the preform 168 resultin a container 100 having thickness and orientation sufficient towithstand hot-filling and distribution through normal chains ofcommerce. The stretching imparted to the material and the clarifyingagents employed in standard materials such as Solvay 4285 facilitatecontainers 100 having low haze values.

In the embodiment of the preform of the present invention depicted inFIGS. 12A and 13A, the wall portion of increased thickness 187represents the thickest portion of the preform blow portion. As bestseen in FIG. 13A and FIGS. 19A-D, the increased thickness of the wallportion of increased thickness 187 provides a reserve of material in thepreform base 180 to insure that the resulting container base is providedwith sufficient material and orientation to resist, for example, dropimpact as well as vacuum resulting from hot-filling procedures. Forexample, the biaxially oriented containers of the present inventionwithstand drop impact 20-30% better than their extrusion blow moldedcounterparts. As discussed below in relation to FIGS. 19A-D, the reserveof material provided by the wall portion of increased thickness 187 islocated in relatively low on the preform 168 and, as a result of theinward curvature of the base portion 180, inward of the outermostdiameter of the preform blow portion. This low and inward location ofthe wall portion of increased thickness 187 allows it to be deposited inthose portions of the base 218 that would otherwise receive insufficientmaterial for purposes of structural rigidity. Specifically, the reserveof material in the wall portion of increased thickness 187 avoidsbecoming caught or hung-up on the annular ribs 226 intruding inward ofthe cylindrical wall 214. The location of the reserve of increasedmaterial thickness in the wall portion 187 circumvents the annular ribs226 during blow molding and is distributed in the base 218. Otherstructural features such as vacuum panels could also be avoided in thismanner and the thickness profile of the preform 168 discussed above canalso be employed for this purpose. While the wall portion of increasedthickness 187 may be located at any distance from the preform outermostdiameter, it is preferred that the upper end of the wall portion ofincreased thickness 187 be located between 0.002 inch (0.00508 cm) and0.015 inch (0.0381 cm) inward of the outermost diameter of the preform.Moving the upper end of the wall portion of increased thickness 187further inward may require too great a thickness of the wall portion 187to allow efficient reheating as discussed below.

The thickness profile can also be employed for containers withoutstructural side wall features such as in the container depicted in FIG.3 to insure that sufficient material is provided to the outer portionsof the container base because regardless of the sidewall features, acontainer base having a foot diameter substantially close to thediameter of the sidewall, such as with the based depicted herein, willcreate a corner with a narrow opening through which sufficient materialmust be blown to create an outer base of the required rigidity. FIG.19C, for example, depicts at least a portion of the wall portion ofincreased thickness 187 of the preform 168 entering an outer portion ofa mold cavity base 546 to form a corresponding container base 216.Without the thickness of the wall portion 187 of increased thickness,the container base 216 might be too thin and weak.

It is contemplated that a wall portion of increased thickness, such asthe wall portion 187 of the preform 168 depicted in FIGS. 12A and 13A,need not be of constant thickness. Rather, the thickness could, forexample, increase slightly from opposing ends to create thicker middleand thinner ends. Other configurations of the wall portion of increasedthickness 187 will become apparent to one of ordinary skill in the artto achieve the above discussed objective of providing a strong containerbase such as container base 216. It is also contemplated that thepreform thickness t3 at the preform axis in the base, need not bethinner than the wall portion of increased thickness t2. The term“increased” in the term “wall portion of increased thickness” isemployed to describe the preferred embodiment discussed above withreference to FIG. 12A. The thickness t3 merely need be designed toinduce sufficient orientation and provide sufficient thickness to thecenter of a resulting container base.

The container 100, as depicted in FIG. 13A, has a finish of equaldimensions to the preform finish 176 because the finish is not subjectedto blow molding as is known to those of skill in the art. The container100 has a blow portion height A, the uppermost end of the cylindricalwall 214 extending to a height of B, and the base 218 extending to aheight of C. The shoulder 212 and base 218 having an outermost diameterof D1 and the cylindrical wall 214 each having an outermost diameter ofD2.

In one embodiment a preform of the configuration of preform 168 havingthe dimensions a=2.317 inch (5.89 cm), b=0.997 inch (2.53 cm), c=0.250inch (0.635 cm), d1=2.480 inch (6.30 cm), t1=0.074 inch (0.188 cm),t2=0.120 inch (0.3048 cm), t3=0.090 inch (0.2286 cm), wherein the outerskin of the wall portion of increased thickness 187 began at an upperend at a distance from the axis 208 in the approximate range of 1.20inch (3.048 cm) and terminated at a lower end at a distance from theaxis 208 in the approximate range of 0.516 inch (1.311 cm), was found tofacilitate blow molding of a strong container 100 having the dimensionsA=3.655 inch (9.28 cm), B=2.200 inch (5.59 cm), C=0.550 inch (1.40 cm),D1=3.090 inch (7.85 cm), D2=3.150 inch (8.00 cm) and a blow portion wallthickness in the range of from 0.025-0.032 inch (0.0635-0.0813 cm).

In the embodiment of the preform of the present invention discussedabove with relation to FIGS. 12A and 13A, the length a of the preformblow portion in relation to the length of the container blow portion Aas well as the location of the reserve of material 187 allows the bodyportion 178 of the preform of the present invention to be substantiallythinner than would be prescribed by known preform design parameters,while maintaining the gram weight necessary to construct the container100. The thinner walls allow a reduced temperature differential betweenthe inner skin and the outer skin during reheating and thus help tofacilitate quicker reheating of the preform to temperatures within theblow process window without reaching the melt temperature.

By way of comparison, FIG. 13B depicts one possible preform 228 designedaccording to standard design techniques for blow molding a PET barriercontainer of the configuration of the container 100. It can be seen bycomparing FIGS. 13A and 13B that PET preform 228 design parametersdictate a preform substantially narrower and shorter than preform 168.As known to those of ordinary skill in the art, PET preforms, includingmultilayer preforms, are designed according to standard designtechniques, to induce a radial stretch ratio of approximately 4.5:1 to5.0:1 and an axial stretch ratio of approximately 2.0:1 to 2.5:1 inorder to strain hardening the preform materials. This typically resultsin an area stretch ratio of roughly 9:1 to 12.5:1.

When indicated herein, the axial stretch ratio shall mean the ratio ofthe length of the blown portion of the container to the length of theblow portion of the preform from which it was blown, both as measuredalong their longitudinal axis. The radial stretch ratio shall mean theratio of the largest outermost diameter of the container blown portionto the inner diameter at the largest outermost diameter of the preformblow portion from which the container was blown. Area stretch ratio, asis known by those of ordinary skill in the art, is the ratio of thecontainer surface area to the preform surface area.

The relatively large axial and/or radial dimensions of the thin walledpreforms, of the present invention dictate a lower stretch ratiocompared to its thicker walled counterparts. It has been found that aradial stretch ratio of at least approximately 1.3:1 and an axialstretch ratio of at least approximately 1.4:1 will produce acommercially acceptable OPP container of the wide-mouth jar typedepicted in FIG. 13A. In one example, a radial stretch ratio ofapproximately 1.3:1 was imparted to the preform 168 in FIG. 19A to reachthe container in FIG. 19D, as was an axial stretch ratio ofapproximately 1.58:1. This resulted in an area stretch ratio ofapproximately 2.1:1.

Preform Injection

The preforms of the present invention may be constructed according tostandard injection molding techniques known to those of ordinary skillin the art such as, by way of example only, the injection moldingtechniques described in U.S. Pat. Nos. 4,511,528 and 4,712,990, theentirety of which are incorporated herein by reference. Thermal gatedinjection molding techniques, known to those of ordinary skill in theart, are also contemplated.

With regard to injection molding barrier preforms according to thepresent invention, it has been found that the injection molding processand equipment is simplified because the ranges of preferred meltprocessing temperatures of PP and EVOH are overlapping. The melt flowtemperatures of both PP and EVOH may be approximately in the range of180-235° C. (more preferably 200-220° C. for PP and 190-210C for EVOH).Therefore, the two materials may be injected at close, or the same,temperatures. Neither the addition of adhesive agents or othermodifications to create enhanced layers, have significantly altered theinjection molding temperature of PP or EVOH. Because little or notemperature difference between the melt materials need be maintained inthe injection equipment, it is relatively easy to maintain proper meltflow temperatures.

It has been found that the objectives of the present invention are morereadily achieved by maintaining homogeneous melt material flow streamsduring injection of the preforms of the present invention such thatfractures of the flow streams are reduced or eliminated. Specifically,it has been found that reducing or eliminating flow stream fracturesincreases the homogeneity of the preform layers, and containers blowntherefrom, and produces a concomitant reduction. Homogeneous flowstreams may be obtained by maintaining the temperature of each flowstreams only slightly above the melt temperature of the polymer. Forexample, a temperature of from 200-260° C. for blow mold gradepolypropylene has been found to assist in maintaining homogeneous flowstreams. Maintaining the flow streams at a slow, constant rate ofinjection has also been found to assist in maintaining theirhomogeneity. For example, an injection cavity fill time of from 3-10seconds for the preform 168 depicted in FIG. 12A has been found toprovide homogeneous flow streams. Injecting the preform 168 at a highcompression ratio also assists in maintaining homogeneous flow streams.A compression ratio of from 3-3.5 has been found beneficial inmaintaining homogeneous flow streams.

It has also been found that a high degree of control over the barrierlayer is desirable during injection to maximize barrier coverage in thepreform. With reference to the preform 168 depicted in FIG. 12A, it hasbeen found desirable to position a finish end 220 of the barrier layer174 as close as possible to an uppermost extremity 222 of the preformfinish 176 as allowed by the barrier flow front uniformity without thebarrier breaking through the uppermost extremity 22 for the reasons ofaesthetics and function discussed above. Flow front uniformity, as isknown to those of ordinary skill in the art, refers to the distancebetween the foremost portion of the barrier leading edge and the aftmostportion of the leading edge. Although a perfectly uniform flowfront isusually desirable, it cannot always be achieved due to various flowdisturbances. Accordingly the barrier will the desired location in someportions of the finish while not in others. An uneven barrier flowfrontcould, therefore, require the absence of barrier at some portions of thefinish 176 in order to prevent barrier break-through at other portions.In one example, it has been found that obtaining complete barriercoverage at a position within 0.100 inches (0.254 cm) from the uppermostextremity 222 of the finish 176, without the barrier layer 174 withoutbreaking through that uppermost extremity, will maintain an acceptableamount of gas migration through a resulting container. It is likewisedesirable to place a base end 224 of the barrier layer as close aspossible to the preform central axis 202 to limit migration of oxygenthrough the base of the container blown from the preform 168. Asdiscussed above, the absence of barrier is substantially less tolerablein a container employing PP than a container employing other materialssuch as PET because of the relatively high permeability of PP by oxygenand carbon dioxide. A high degree of control over the barrier layer 174may be maintained with standard apparatus and methods known to those ofordinary skill in the art. For example, it has been found that thebarrier fold-over injection method disclosed in U.S. Pat. No. 4,554,190,the entirety of which is incorporated herein by reference, affords theability to locate the barrier close to the finish uppermost extremity222. Other contemplated injection methods will be recognized by those ofordinary skill in the art.

The condition of the injection cavity, which receives the melt materialflow streams to form a preform according to the present invention, mayalso assist in reducing haze of a container blown from that preform.Specifically, decreasing the cooling time of the preform, such as bymaintaining the injection cavity relatively cold, will limit oreliminate the time in which growth of spherulites is possible in the PP.For example, maintaining the injection cavity at a temperature of from0-30° C. assists in cooling a preform of the present invention quicklyenough to prevent the growth of spherulites in the PP when the meltmaterials are injected at 180-235° C. over a fill time of fromapproximately 3.0-10.0 seconds. Additionally, it has been found thatemploying an injection cavity having polished mold surfaces also assistsin clarifying the container blow molded therefrom.

Reheat

The low thermal conductivity, high heat capacity and narrow blow processwindow (preferably 125-132° C.) of PP presents a unique difficulty inthe reheating of a PP preform for blow molding. One known method ofreheating a PP preform, as depicted in FIG. 14, is the simpleheat-equilibrate method which comprises subjecting the outer skin of thepreform to infrared radiation to raise the preform outer skintemperature To to a temperature above the target blow moldingtemperature Tb, then removing the preform from exposure to infraredradiation when the temperature To has reached a temperature Tmax thatwill elevate, via conduction, the remainder of the preform material tothe blow molding temperature Tb at the time the temperature To hascooled to the blow molding temperature Tb. In this manner, the preformis uniformly brought to the blow molding temperature Tb. The temperatureversus time diagram in FIG. 14 depicts the relation of the outer skintemperature To and the inner skin temperature Ti with respect to theblow molding temperature Tb over time as the preform is heated fromambient temperature to a uniform blow molding temperature Tb. Whenreheating a PP preform, the upper limit of Tmax is constrained only bythe melt temperature of the outer layer. By way of example, the melttemperature of Solvay 4285 PP is roughly 160° C. If the melt temperatureis exceeded, the preform may deform or collapse. Moreover, when the PPreaches its melt temperature, the molecules are freed to form largercrystals upon cooling than would be found in a PP reheated to the blowprocess temperature and blown.

The difficulties associated with reheating PP preforms are exacerbatedby the addition of an intermediate layer to the preform which divides amajority of the PP into an inner layer and an outer layer as, forexample, in the preforms depicted in FIGS. 11, 12A and 12B. First, theaddition of an intermediate layer will prevent some of the infraredradiation directed at the outer skin of the preform from reaching theinner layer. This is due, at least in part, to absorption by theintermediate layer as well as reflection and refraction at theinterfaces of the intermediate layer and each of the inner and outerlayers. Because typical reheat equipment directs infrared radiation atthe outer skin of the preform, the inner layer of a preform having anintermediate layer will gain less heat from the infrared radiation ofthis typical reheat equipment. The inner layer must then rely, at leastin part, on heat conduction from the outer layer and the intermediatelayer to approach the temperature of the outer layer. Therefore, amultilayer preform, such the preform 168 depicted in FIG. 12A, willrequire a greater amount of heat conduction from the outer layer to theinner layer than a mono-layer preform. Depending on the material andthickness of the intermediate layer, the two step heat-equilibratemethod diagramed in FIG. 14 may require a Tmax greater than the melttemperature of the outer layer.

One aspect of the present invention entails a reheat method depicted inthe temperature versus time diagram of FIG. 15. The diagram of FIG. 15depicts the relation of the outer skin temperature To and the inner skintemperature Ti with respect to the blow molding temperature Tb over timeas the preform is reheated from ambient temperature to a blow moldingtemperature Tb which may be a range such as the preferred PP blowmolding process window of 125-132° C. The diagram in FIG. 15 alsodepicts the melt temperature Tmelt which the outer skin should notreach. The temperature Tmax may vary from manufacturer to manufacturerand from grade to grade as will be recognized by one of ordinary skillin the art.

With reference to the diagram of FIG. 15, the reheat method of thepresent invention comprises three stages. Stage 1 comprises elevatingthe outer skin temperature To approximately to a temperature Tmax thatis below the Tmelt temperature, preferably staying at leastapproximately 10° C. below the Tmelt temperature for safe measure. Stage2 comprises maintaining the outer skin temperature To at approximatelyTmax for a period of time allowing the heat from the outer layer to beconducted through the barrier layer, into and through the inner layer tothe inner skin, raising the inner skin temperature Ti as depicted. Theouter skin temperature To will likely vary slightly throughout Stage 2rather than remaining perfectly constant. However, by maintaining theouter skin temperature To at this elevated Tmax through Stage 2,sufficient heat will be conducted from the outer layer to the innerlayer to compensate for the infrared radiation blocked by the additionof the intermediate layer. Stage 3 comprises allowing the out skintemperature To to reduce to the blow temperature Tb while the preformsettles uniformly into the blow temperature Tb. Each stage can compriseone or more reheat ovens or, in the case of the final stage, no reheatoven may be necessary.

In one embodiment of a reheating apparatus for a PP preform according tothe method diagramed in FIG. 15 and described above, FIG. 16 depicts areheat apparatus having a frame 502 supporting a conveyor 504 forholding and conveying a series of preforms 506 past a series of reheatovens 508. The series of reheat ovens 508 can be of the infraredradiation type or other type of reheat oven known in the art. However,infrared reheat ovens are depicted for purposed of explanation. As isstandard in the art, each preform 506 is separately held on the conveyor504 by a preform mount 510 which accepts the finish portion of acorresponding preform and imparts a rotation to the preform about itslongitudinal axis so as to expose the outer skin of the preform toradiation from the series of reheat ovens 508 at all 360° of the preformabout its longitudinal axis. The series of reheat ovens 508 are arrangedin the numbers, and set at the powers necessary, to accomplish thereheating of the preforms as diagramed in FIG. 15. For example, Stage 1of the reheat process diagramed in FIG. 15 could be accomplished by thefirst reheat oven 512 of the series of reheat ovens 508 depicted in FIG.16. Stage 2 could be accomplished by the second and third reheat ovens514, 516. In one embodiment, the second and third reheat ovens 514, 516are set at lower power settings than the first reheat oven 512 becausethe second and third ovens 514, 516 need only maintain temperature To ata given temperature Tmax while the first reheat oven 512 is required toelevate the outer skin temperature from ambient temperature to Tmax. Inthis embodiment, Stage 3 is accomplished by the fourth reheat oven 518.In one embodiment, the fourth reheat oven 518 is set at a lower powersetting than that of the second and third ovens 514, 516, and possible azero power setting, to allow the temperatures To and Ti to approach toTb. Because Stage 2 must elevate the inner layer temperature at least inpart by conduction rather than through infrared radiation, and with asmall heat differential (Tmelt=160° C. whereas the preferred Tb=128-132°C.), it is contemplated that Stage 2 will require a longer period oftime than either Stage 1 or Stage 2. It is also contemplated that thenumber of reheat ovens and oven powers can be modified to achieve thereheat process diagramed in FIG. 15.

The specifics of the necessary number and length of the reheat ovens,the infrared radiation bulb configurations in each bed and the power ofeach bulb, is dictated by the specific material of the various layers ofthe preform, the various thicknesses and thickness profiles of thepreform and the desired blow molding temperature to which they will beelevated. While the below examples discuss preforms of particularconfigurations and materials, the reheat process described herein may beemployed with monolayer or multilayer preforms of any configuration toachieve a preform reheated to within the blow molding process windowwithout reaching the melt temperature of the preform materials.

The relatively thin blow portion of the preform 168 of the presentinvention reduces the total time necessary to reheat the preform 168 intwo ways. First, it places more of the material which constitutes theouter layer 172 on the surface of the preform creating more materialexposed to direct infrared radiation. Second, it brings the inner skincloser to the outer skin and lessens the material through which the heatmust be conducted. Reducing the reheat time is beneficial to theeconomics of manufacturing.

Reheating of preforms constructed according to the present invention canbe accomplished with reheat bulb configurations arranged according toprincipals known in the art for reheating monolayer OPP preforms or PETpreforms of either monolayer or multilayer configuration. FIG. 17depicts one reheat bulb configuration for reheating the preform 168 ofFIG. 12A of the present invention. The reheat oven 520, which couldconstitute any one or more of the ovens 512, 514, 516 or 518, has fivereheat elements 522, 524, 526, 528 and 530, that are preferably infraredbulbs and configured as depicted along the blow section of the preform168 having the wall portion of increased thickness 187. The bulbs 522,524, 526, 528 and 530 are positioned with respect to the preform 168 soas to heat adjacent portions thereof. The first bulb 522 radiates theneck 186 and shoulder 184. The second bulb 524 radiates the neck 186,shoulder 184 and a portion of the cylindrical sidewall 182. The thirdbulb 526 radiates the cylindrical sidewall 182 and a small portion ofthe base 180. The fourth bulb 528 is positioned so that it almostexclusively radiates the wall portion 187 of increased thickness t2. Thefifth bulb 530 radiates the very tip of the preform as depicted.

The fourth bulb is provided an almost exclusive ability to radiate thearea of increased thickness 187 so that the increased radiation neededto reheat this area of increased thickness 187 can be provided withoutelevating the temperature of the thinner portion of the base 180 at theaxis 208 or the thinner body portion 178 above the melt temperatures.The fourth bulb 528 can be positioned slightly closer to the preformthan proscribed by standard reheat bulb configurations in order toconcentrate the radiation from that bulb on the area of increasedthickness 187 and limit or prevent overflow of radiation to otherportions of the preform.

REHEAT—EXAMPLE 1

By way of example, one embodiment of the reheat method of the invention,as represented in FIG. 18, comprised reheating a series of preforms 532of the size and shape of the preform 168 depicted in FIGS. 12A and 13Afor blow molding into a container of the size and shape of the container100 depicted in that FIG. 13A. The wall thickness of the preform 168 inthis example is as specifically set forth above for FIGS. 12A and 13A.The barrier segregates the sidewall into an inner layer and an outerlayer of approximately equal thicknesses. In the embodiment of thepreform 168 reheated in this example, the inner and outer layerscomprised 85% Solvay 4285 PP and 15% Tymor 2E02 adhesive agent blendedtherein. The barrier layer employed in the example below comprisedEvalca F-104BW EVOH.

In this example, the reheat ovens were standard ovens from a Sidel SBO8/16 blow molding machine, as will be know to those of ordinary skill inthe art. Each bed was set one immediately next to the other, asdepicted, so that no gap existed therebetween and the preforms beingconveyed thereby were exposed to continuous infrared radiation. Forsimplicity, each in the series of ovens comprised five infraredradiation bulbs configured as described in relation to FIG. 17, eachspaced a vertical distance of 15 mm on center from the bulbsthereadjacent. The preforms were conveyed past the ovens at a rate of0.14 meters per second for a total continuous reheat time of 42 seconds.The bulbs were at the following powers for each oven: Bulb 1—95%; Bulb2—75%; Bulb 3—35%; Bulb 4—55%; Bulb 5—40%.

The preforms 520 in this example achieved a substantially uniform reheattemperature of approximately 130° C. after passing the series of ovensaccording to the above parameters.

Although the each reheat bed in this example comprised an identical bulbconfiguration for purposes of simplicity, variation of the bulbconfigurations from one heat bed to the next is contemplated to achievethe objectives of reheating a multilayer preform approximately accordingto the principals set forth in the diagram of FIG. 15.

REHEAT—EXAMPLE 2

Alternatively, it has been found that the reheat methods disclosed inU.S. Pat. Nos. 5,066,222 and 5,326,258, the entireties of which areincorporated herein by reference, may reheat a the preform described inReheat Example 1 to a blow temperature of approximately 130° C. withoutsurpassing the approximate 160° C. melt temperature of Solvay 4285. Forexample, as with Example 1, a series of preforms 532 of the size andshape of the preform 168 discussed in relation to FIGS. 12A and 13A forblow molding into a container of the size and shape of the container 100discussed in relation to FIG. 13A. The barrier segregates the sidewallinto an inner layer and an outer layer of approximately equalthicknesses. In the embodiment of the preform 168 reheated in thisexample, the inner and outer layers comprised 85% Solvay 4285 PP and 15%Tymor 2E02 adhesive agent blended therein. The barrier layer employed inthe example below comprised Evalca F-104BW EVOH.

In this example, the reheat ovens were standard ovens from a Bekum RBU225 blow molding machine, as will be know to those of ordinary skill inthe art. Each bed was set one immediately next to the other, asdepicted, so that no gap existed therebetween and the preforms beingconveyed thereby were exposed to continuous infrared radiation. Forsimplicity, each in the series of ovens comprised five infraredradiation bulbs configured as depicted in FIG. 17 each spaced a verticaldistance of 15 mm on center from the bulbs thereadjacent. The preformswere conveyed past the ovens at a rate of 0.011 m/s for a totalcontinuous reheat time of 72 seconds. The bulbs were at the followingpowers for each oven: Bulb 1—65%; Bulb 2—35%; Bulb 3—37%; Bulb 4—30%;Bulb 5—67%.

The preforms in this example achieved a substantially uniform reheattemperature of approximately 130° C. after passing the series of ovensaccording to the above parameters.

Although the each reheat bed in this example comprised an identical bulbconfiguration for purposes of simplicity, variation of the bulbconfigurations from one heat bed to the next is contemplated to achievethe objectives of reheating a multilayer preform approximately accordingto the principals set forth in the diagram of FIG. 15.

Blow Molding

Blow molding preforms constructed according to the present invention isaccomplished according to standard blowing techniques known in the artfor blow molding monolayer OPP and monolayer and multilayer PET,adjusted to accommodate blow processing window of PP. Differencesbetween PP and PET, particularly the difference in the amounts ofstretching required for strain hardening, create difficulties in“moving” material past mold cavity intrusions from the sidewall such asthe window panels 44 of the container 28 depicted in FIG. 2, the windowpanels 78 of container 62 depicted in FIG. 4A, the window panels 96 ofcontainer 80 depicted in FIG. 4B, and the annular ribs 116 of thecontainer 100 depicted in FIGS. 5, 6 and 13A.

It has been found that blow molding a PP preform of uniform thickness ina mold cavity having such intrusions will cause material to becomecaught on the intrusions. The preform then will have insufficientmaterial left to mold a container base of the desired thickness. Thepreform thickness profile of the present invention, one embodiment ofwhich is discussed in relation to FIG. 12A, overcomes this problem byplacing the wall portion of increased thickness 187 in and about theportion of the preform that will become the contact ring of thecontainer base. Because the wall portion of increased thickness 187 islocated on an inwardly curved base of preform, it does not contact thevarious intrusions of the type depicted in FIGS. 2, 4A, 4B and 5 duringblow molding. Rather, as depicted in FIGS. 19A-19D, which exhibitvarious stages of blow molding the preform 168 depicted in FIG. 12A intothe container 100 depicted in FIGS. 5,6 and 13A, the wall portion ofincreased thickness 187 avoids these intrusions and is placed in thebase. Without increased volume of material in the wall portion ofincreased thickness 187, the base foot would have insufficient materialto make the base foot of similar thickness to the remainder of thecontainer.

FIGS. 19A-19D depict various stages of the preform 168 being inflated toconform to the a mold cavity 534 having a finish 536 identical to thatof the preform 168, a neck 538, a shoulder 540, a cylindrical wall 542with annular ribs 544 and a base 546 having a foot 548. FIG. 19A depictsthe preform 168 accommodated within the mold cavity 534 and oneembodiment of the stretchrod of the present invention 550, describedbelow, is in contact with the base 180 of the preform 168. The preform168 has been reheated to an appropriate blow molding temperature. FIG.19B depicts the stretchrod 550 having axially stretched the preform 168and blow air having started the inflation of the preform 168. FIG. 19Cdepicts the cylindrical wall of the preform inflated against thecylindrical wall of the mold cavity 542 and the preform wall portion ofincreased thickness 187 positioned to be blown into the foot 548 of themold cavity to form the container foot. FIG. 19D depicts the resultingcontainer 100 conformed to the mold cavity 534 and the stretchrod 550retracting back out of the mold cavity in preparation for expulsion ofthe container 100 from the cavity 534 and the accommodation of asubsequent preform for blow molding. As can be seen in FIGS. 19A-19D,due to the proximity of the preform wall portion of increased thickness187 to the central axis 208 of the preform 168, as well its proximity tothe base 546 of the cavity 534, the wall portion 187 of increasedthickness t2 in the base 180 of the perform 168 does not come intocontact with the intruding annular ribs 116. Rather, the wall portion187 of increased thickness t2 is positioned in and around the foot 548of the cavity base 546 to strengthen the base 106 of the resultingcontainer 100. In this manner, the preform thickness profile of thepresent invention has overcome the difficulties with moving PP in a moldcavity. Despite the variation of the preform wall thickness, theresulting container 100 comprises a relatively constant thicknessthroughout the body 104 and base 106.

Certain general blow molding process parameters have also been found tofacilitate molding the container 100 consistent with the objectives ofthe present invention from the above-described preform 168. For example,no preblow is needed when blowing the preform of FIGS. 12A and 13A intothe container depicted in FIG. 13A because the preform needs littleradial enlargement.

BLOW MOLDING EXAMPLE 1

In one embodiment, a Bekum RBU225 blow molding machine was employed toblow barrier PP preforms of the type depicted in FIGS. 12A and 13A andof the dimensions set forth therein were reheated in a standard Bekumreheat oven to a temperature in the range of approximately 128-132° C.throughout the entire blow portion of the preform using the methoddescribed in U.S. Pat. Nos. 5,066,222 and 5,326,258. The preforms wereblown into containers of the configuration depicted in FIGS. 6 and 13A,and of the preferred dimensions discussed in relation thereto, wasaccomplished with a blow air pressure of approximately 11 bar (159.5psi) and with no delay between the initiation of blow air and initiationof axial elongation of the preform with the stretchrod. The blow air washeld for 2.5 seconds.

The resulting container comprised a thickness throughout the body andbase ranging from 0.025 inch (0.0635 cm) to 0.033 inch (0.0838 cm).

Stretchrod

It has been found that preforms constructed according to the presentinvention may tend to adhere to a stretchrod of standard constructionwhen allowed to be elevated to high temperatures as a result ofcontinuous blow molding at commercial production frequencies with thesame stretchrod. FIG. 20 depicts the effect of this adhesion with astandard stretchrod 552 having a standard tip. As depicted in FIG. 20,when the stretchrod 552 adheres to the enhanced PP at the gate area 554of the blown container 556, the stretchrod 552 pulls the gate area 554of a resulting container 556 back into the volume of the container 556as the stretchrod 552 retreats from the mold cavity 558 in preparationfor the mold receiving a subsequent preform for molding. The deformedcontainer gate area 554 weakens the base of the container 556 renderingit defective for commercial applications. The resulting aesthetics alsorender the container 556 defective.

It is believed that adhesion between the preform and a standardstretchrod, such as stretchrod 552, tends to occur as the stretchrodapproaches the PP blow temperature. In one embodiment, sticking has beenfound to begin after continuous blow molding at a blow temperature ofapproximately 131° C. Blowing containers at a high frequency provides astandard stretchrod inadequate time to cool between cycles. Aftercontinued operation, the standard stretchrod 552, and most importantlythe stretchrod tip, approaches the blow molding temperature of PP asheat is transferred from the preform to the stretchrod by conduction andconvection. The temperature reached by any given stretchrod for a givenpreform temperature and given molding frequency will be referred toherein as the steady state temperature of the stretchrod.

By way of example, adherence was witnessed when employing a standardsteel 18 mm stretchrod in a Bekum RBU225 blow molding machine blowing120 consecutive preforms constructed of 85% Solvay 4285 PP with 15%Tymor 2E02 adhesive grafted thereto, wherein the preforms were reheatedto a temperature of approximately between 130-132° C. Although loweringthe reheated temperature of the preforms would lower the steady statetemperature of this stretchrod, it could also cause fracture of the PPchains in the base, reducing the structural strength thereof. In extremecases, reducing the blow molding temperature of the preforms could causethe stretchrod to rupture the preform during axial elongation. Strainhardening would also be affected.

The stretchrod of the present invention maintains a steady statetemperature sufficiently cooler than the blow molding temperature of PPto prevent sticking by, in part, being comprised of a material having ahigh thermal conductivity, such as aluminum. Additionally, the size ofthe stretchrod tip is increased to increase its surface area and, thus,the rate of convection to cool the stretchrod tip. The surface area ofthe tip backside (i.e. the side that does not contact the preforms) mayoptionally be provided with one or more features to increase its surfacearea and, therefore, its rate of convection. In one embodiment, FIG. 21depicts a stretchrod 560 of the present invention having a mushroom-typetip 562. The mushroom-type tip 562 is also depicted in FIGS. 22A and22B. The tip 562 is round and symmetrical about its longitudinal axis564. The tip 562 comprises a threaded attachment insert 566, forthreading into the stretchrod 560, and a disk 568. The disk 568comprises an arcuate stretching surface 570, an annular wall 572 and abackside 574. The arcuate stretching surface 570 is constructed to havea radius of curvature approximating that of the preform surface withwhich it is intended to have contact. In one embodiment of the presentinvention, a preform tip 562 employed to stretch the preform 168 in FIG.12A has an outer diameter of 0.985 inch (2.50 cm) when the outerdiameter of the preform 168 is 2.48 inch (6.30 cm). The backside 574 isoptionally provided with a number of holes 576 to increase the backsidesurface area and provide a concomitant increase in the potential rate ofheat convection from the tip 562. The holes 576 are dispersed about thebackside 574 between the annular wall 572 and an outline 578 of theinterface between the backside 574 and the stretchrod 560. Alternativemanners of increasing the surface area of the tip backside 574 are alsocontemplated. For example, fins (not depicted) could be configured toextend from the backside 574 or grooves (not depicted) could be cut intothe backside. Other configurations to increase the surface are of thebackside 574 will be recognized by one of ordinary skill in the art.

It has also been found that the large stretching surface 570 decreasesthe stress in those portions of the preform directly contacting thestretchrod tip 562. Fracture of the preform material is thereby reduced.

In one embodiment, the stretchrod tip 562 is larger than the hole in thebarrier layer of the preform, if any, at the gate of the preform. It isbelieved that if the stretchrod tip 562 directly contacts the portion ofthe preform inner layer directly adjacent to the at least the base endof the barrier layer, then the stretchrod tip 562 will itself impartaxial elongation to the barrier layer rather than relying on theadhesive force between the barrier layer and the inner and outer layersto transmit the force from the stretchrod tip 562.

Haze

In addition to structural rigidity and barrier protection, thecontainers of the present invention have a low haze value. A haze valueis defined as the percent of total light which, in passing through thespecimen, deviates through forward scatter by more than 0.044 rad (2.5°)on the average. The preferred test to obtain the haze value of thebottle is ASTM Method D-1003 as defined in the 1995 Annual Book of ASTMStandards, Volume 8.01. It is believed that stretching of PP breaks downcrystals found in the semi-crystalline material from which injectionmolded preforms are comprised. As the size of the crystals are reducedin a layer of that material, so is the amount of light scattered by thatlayer. Although the size of PP crystals in amorphous PP comprising aclarifying agent are smaller than crystals in amorphous PP notcomprising a clarifying agent, a reduction in crystal size will also beexperienced with clarified PP as a result of stretching. In oneembodiment, the containers of the present invention have a haze value ofless than approximately 20% in their sidewall. In another embodiment,the bottles have a haze value of 10-12% in at least the sidewallthereof.

It will be understood by those of ordinary skill in the art that thefinish of the container will have a higher haze value than the sidewallbecause no stretching is induced therein. Similarly, the centermostportions of the container base will have a higher haze value than thesidewall because little stretching is typically induced therein.Beneficially, those portions of the container that have been provided nostretching (as in the finish) or little stretching (as in the base), areclearer than their non-clarified counterparts.

HAZE EXAMPLE 1

By way of example, a container of the configuration depicted in FIG. 13Aand described herein having enhanced PP layers comprising Solvay 4285 inthe amount of 85% by weight and Tymor 2E02 in the amount of 15% byweight and having a total wall thickness of from 0.025-0.028 inch,having a barrier layer comprising Evalca F104BW EVOH with a thickness ofapproximately 0.0015, was blown from the preform depicted in FIG. 12A atthe blow process temperature of approximately 128° C. to form acontainer having haze value of approximately less than 20% in the bodyportion thereof.

HAZE EXAMPLE 2

A container of the configuration depicted in FIG. 13A and describedherein having enhanced PP layers comprising Solvay 4285 in the amount of90% by weight and Tymor 2E02 in the amount of 10% by weight and having atotal wall thickness of from 0.025-0.028 inch, having a barrier layercomprising Evalca F104BW EVOH with a thickness of approximately 0.0015inch was blown from the preform depicted in FIG. 12A at the blow processtemperature of approximately 128° C. to form a container having hazevalue of approximately less than 20% in the body portion thereof.

HAZE EXAMPLE 3

A container of the configuration depicted in FIG. 13A and describedherein having enhanced PP layers comprising Solvay 4285 in the amount of85% by weight and Tymor 2E04 in the amount of 15% by weight and having atotal wall thickness of from 0.025-0.028 inch, having a barrier layercomprising Evalca F104BW EVOH with a thickness of approximately 0.0015inch, was blown from the preform depicted in FIG. 12A at the blowprocess temperature of approximately 128° C. to form a container havinghaze value of approximately less than 20% in the body portion thereof.

HAZE EXAMPLE 4

A container of the configuration depicted in FIG. 13A and describedherein having enhanced PP layers comprising Solvay 4285 in the amount of90% by weight and Tymor 2E04 in the amount of 10% by weight and having atotal wall thickness of from 0.025-0.028 inch, including a barrier layercomprising Evalca F104BW EVOH with a thickness of approximately 0.0015inch, was blown from the preform depicted in FIG. 12A at the blowprocess temperature of approximately 128° C. to form a container havinghaze value of approximately less than 20% in the body portion thereof.

HAZE EXAMPLE 5

A container of the configuration depicted in FIG. 13A and describedherein having enhanced PP layers comprising Solvay 4285 in the amount of95% by weight and Fusabond 353D in the amount of 5% by weight and havinga total wall thickness of from 0.025-0.028 inch, having a barrier layercomprising Evalca F104BW EVOH with a thickness of approximately 0.0015inch, was blown from the preform depicted in FIG. 12A at the blowprocess temperature of approximately 128° C. to form a container havinghaze value of approximately less than 15% in the body portion thereof.

HAZE EXAMPLE 6

A container of the configuration depicted in FIG. 13A and describedherein having enhanced PP layers comprising Solvay 4285 in the amount of97% by weight and Fusabond 353D in the amount of 3% by weight and havinga total wall thickness of from 0.025-0.028 inch, having a barrier layercomprising Evalca F104BW EVOH with a thickness of approximately 0.0015inch was blown from the preform depicted in FIG. 12A at the blow processtemperature of approximately 128° C. to form a container having hazevalue of approximately less than 15% in the body portion thereof.

EXAMPLES OF CONTAINER CONSTRUCTION

Enhanced PP Layers/Non-enhanced Barrier Layer

The amount of adhesive agent blended into the base polypropylene dependson the maleic anhydride concentration of the adhesive. While otherconcentrations are contemplated, it has been found that, typically,enough adhesive agent must be added to the PP such that the resultingenhanced PP has a maleic anhydride content of approximately between0.01%-0.20% by weight of the enhanced PP. For example: 10% of anadhesive agent containing 0.15% maleic anhydride would provide a maleicanhydride content of 0.015% by weight. As discussed above, the greaterthe percentage of maleic anhydride or other adhesive used, the betterthe barrier layer will adhere to the structural layers.

The following are representative examples of the structures contemplatedas having enhanced PP layers and a non-enhanced barrier layer.

Construction Example 1

A three-layer injection molded preform was made having inner and outerlayers made from an enhanced PP containing about 85% PP and 15% adhesiveagent blended therein and a barrier layer between the inner and outerlayers. The PP was Solvay 4285. The adhesive agent was Tymor 2E02. Thebarrier layer was Evalca LCE-105A EVOH (having a 44% ethylene content).The preform was then stretch blow molded to form a substantiallytransparent container having a haze value of approximately 10-12%measured through a section of the container having a thickness ofapproximately 15-20 mils.

Construction Example 2

A three-layer preform was injection molded as in Example 1 except thatthe percentages of PP and adhesive agent in the inner and outer layerswere 90% PP and 10% adhesive agent blended therein. The preform wasstretch blow molded to form a substantially transparent container havinga haze value of approximately between 10-12% measured through a sectionof the container having a thickness of approximately 15-20 mils.

Construction Example 3

A three-layer container was made by a coextrusion blow molding processwherein the layers were extruded together as a tube which was then blowmolded to form the container. The inner and outer layers were made froman enhanced PP containing about 90% PP and 10% adhesive agent blendedtherein. The PP was Montel SR256M. The adhesive agent was Tymor 2E02.The barrier layer was comprised of Evalca LCE-105A EVOH.

Construction Example 4

A three-layer preform was injection molded as in Example 1 except thatthe EVOH used was Evalca LCF-104AW (having a 32% ethylene content). Thepreform was then stretch blow molded to form a low haze container.

Construction Example 5

A three-layer preform was injection molded as in Example 1 except thatthe EVOH used was Evalca LCL 101A (having a 27% ethylene content). Thepreform was then stretch blow molded to form a low haze container.

Construction Example 6

A three-layer preform was injection molded as in Example 1 except thatthe EVOH used was Nippon Gohsei Soamol DC3203. The preform was thenstretch blow molded to form a substantially low haze container.

Construction Example 7

A three-layer preform was injection molded as in Example 1 except thatthe barrier material was comprised of Mitsubishi's MXD6-6121 nylon. Thepreform was then stretch blow molded to form a low haze container.

Construction Example 8

A three-layer preform was injection molded as in Example 1 except thatthe PP was Fina 7426MZ. The preform was then stretch blow molded to forma low haze container.

Construction Example 9

A three-layer preform was injection molded as in Example 1 except thatthe PP was Montel SR256M. The preform was then stretch blow molded toform a low haze container.

Construction Example 10

A three-layer preform was injection molded as in Example 1 except thatthe inner and outer layers were 100% Mitsui Admer QB510A. The preformwas then stretch blow molded to form a low haze container.

Construction Example 11

A three-layer preform was injection molded as in Example 1 except thatthe percentages of PP and adhesive agent in the inner and outer layerswere comprised of 90% PP and 10% adhesive agent blended therein, whereinthe PP was Solvay 4285, the adhesive agent was DuPont Bynell 50E571 andthe EVOH was Evalca LC-E105. The preform was then stretch blow molded toform a low haze container.

Construction Example 12

A three-layer preform was injection molded as in Example 11 except thatthe EVOH was Evalca F104BW. The preform was then stretch blow molded toform a low haze container.

Construction Example 13

A three-layer preform was injection molded as in Example 11 except thatthe PP was Amoco 8649-X, the adhesive agent was Tymor 2E02 and the EVOHwas Evalca LC-E105A. The preform was stretch blow molded to form a lowhaze container.

Construction Example 14

A three-layer preform was injection molded as in Example 11 except thatthe PP was Amoco 8649-X, the adhesive agent was Tymor 2E02 and the EVOHwas Evalca F104BW. The preform was stretch blow molded to form a lowhaze container.

Construction Example 15

A three-layer preform was injection molded as in Example 2 except thatthe EVOH was Evalca LC-E105. Interlayer adhesion was obtained. Nocontainer was blown.

Construction Example 16

A three-layer preform was injection molded as in Example 2 except thatthe PP was Montel X-11651 and the EVOH was Evalca F104BW. The preformwas stretch blow molded to form a low haze container.

Construction Example 17

A three-layer preform was injection molded as in Example 1 except thatthe inner and outer layers were comprised of 80% PP, 10% adhesive agentand 10% EVOH. The PP was Solvay 4285. The EVOH was Evalca F104BW. Theadhesive agent was DuPont Bynell 50E571. Interlayer adhesion wasobtained. No container was blown.

Construction Example 18

A three-layer preform was injection molded as in Example 1 except thatthe EVOH was Evalca 104BW. The preform was stretch blow molded to form alow haze container.

Construction Example 19

A three-layer preform was injection molded as in Example 18 except thatthe adhesive agent was Tymor 2E04. The preform was stretch blow moldedto form a low haze container.

Construction Example 20

A three-layer preform was injection molded as in Example 19 except thatthe EVOH was Evalca XEP-561. The preform was stretch blow molded to forma low haze container.

Construction Example 21

A three-layer preform was injection molded as in Example 19 except thatthe EVOH was Evalca XEP-719. The preform was stretch blow molded to forma low haze container.

Construction Example 22

A three-layer preform was injection molded as in Example 19 except thatthe EVOH was Evalca XEP-721. The preform was stretch blow molded to forma low haze container.

Construction Example 23

A three-layer preform was injection molded as in Example 19 except thatthe EVOH was Evalca ETC-127. The preform was stretch blow molded to forma low haze container.

Construction Example 24

A three-layer preform was injection molded as in Example 19 except thatthe EVOH was SoarusD2908. The preform was stretch blow molded to form alow haze container.

Construction Example 25

A three-layer preform was injection molded as in Example 19 except thatthe EVOH was Soarus SG430. The preform was stretch blow molded to form alow haze container.

Construction Example 26

A three-layer preform was injection molded as in Example 19 except thatthe barrier material was Grivory G21 nylon. The preform was stretch blowmolded to form a low haze container.

Construction Example 27

A three-layer preform was injection molded as in Example 19 except thatthe barrier material was Mitsubishi MxD6 type 6001 nylon. The preformwas stretch blow molded to form a low haze container.

Construction Example 28

A three-layer preform was injection molded to have inner and outerlayers made from an enhanced PP, containing about 90% PP and 10%adhesive agent blended therein, and a barrier layer between the innerand outer layers. The PP was Solvay 4285. The adhesive agent was Tymor2E07-3. The barrier layer was Evalca F-104BW EVOH. The preform was thenstretch blow molded to form a substantially transparent container havinga low haze value.

Construction Example 29

A three-layer preform was injection molded to have inner and outerlayers made from an enhanced PP, containing about 95% PP and 5% adhesiveagent blended therein, and a barrier layer between the inner and outerlayers. The PP was Solvay 4285. The adhesive agent was Fusabond 353D.The barrier layer was Evalca F-104BW EVOH. The preform was then stretchblow molded to form a substantially transparent container having a lowhaze value.

Construction Example 30

A three-layer preform was injection molded as in Example 29 except thatthe barrier layer was Evalca ETC-127 EVOH. The preform was stretch blowmolded to form a low haze container.

Construction Example 31

A three-layer preform was injection molded as in Example 29 except thatthe adhesive agent was Fusabond 411D. The preform was stretch blowmolded to form a low haze container.

Construction Example 32

A three-layer preform was injection molded as in Example 29 except thatthe adhesive agent was Fusabond 536D. The preform was stretch blowmolded to form a low haze container.

Construction Example 33

A three-layer preform was injection molded as in Example 29 except thatthe barrier layer was 22X17-5 and the Fusabond 353D adhesive agent waspresent in the enhanced PP layer in the amount of about 2% while theSolvay 4285 PP was present in the amount of about 98%. The preform wasstretch blow molded to form a low haze container.

The bottles achieved in the above Examples 1-14, 16 and 18-33 exhibitlow haze values, good strength and provide carbon dioxide, oxygen andmoisture barrier.

Non-enhanced PP Layers/Enhanced Barrier Layer

The following are representative examples of the structures contemplatedas having an enhanced barrier layer and non-enhanced structural layers.

Construction Example 34

A three-layer preform was injection molded having inner and outer layersmade from 100% Solvay 4285 PP and a barrier layer between the inner andouter layers. The barrier layer was made from 100% Evalca XEP403 resin.The preform was then stretch blow molded to form a low haze container.

Construction Example 35

A preform was made as in Example 1 except that the PP used for thestructural layers was Fina 7426MZ and the barrier layer was comprised ofEvalca XEP403 EVOH having 100 ppm of Cobalt. The preform was thenstretch blow molded to form a low haze container.

Construction Example 36

A preform was made as in Example 1 except that the PP used for thestructural layers was Fina 7635XM Clear Polypropylene.

Construction Example 37

A preform was made as in Example 1 except that the barrier layer wascomprised of 98% Evalca F-104BW EVOH with 2% Fusabond 353D adhesiveagent blended therein. The preform was then stretch blow molded to forma low haze container.

The bottles made in the above Examples 34-37 above exhibited low haze,good strength and carbon dioxide, oxygen and moisture barrierprotection.

Enhanced PP Layers/Enhanced Barrier Layer

Construction Example 38

A three-layer preform was injection molded having enhanced structurallayers comprising from 95% Solvay 4285 PP with 5% Tymor 2E02 blendedtherein. The enhanced barrier layer comprised 50% Evalca F104BW EVOH and50% Tymor 2E02 blended therein. The preform exhibited excellentinterlayer adhesion. No container was blown.

1-48. (canceled)
 49. An injection molded preform for reheat stretch blowmolding a container comprising polypropylene and having a finish, a neckextending from the finish, a sidewall extending from the neck and a baseextending from the sidewall, the preform comprising a finish having asupport flange, and a preform blow section having a neck extending fromthe support flange, a sidewall extending from the neck and a baseclosing the blow section, the preform sidewall having a thickness atleast approximately 2.3 times the thickness of the container sidewall.50. The preform of claim 49, the preform sidewall having a thickness atleast 2.5 times the thickness of the container sidewall.
 51. The preformof claim 49, the preform sidewall having a thickness at least 2.7 timesthe thickness of the container sidewall.
 52. The preform of claim 49,the average thickness of the preform sidewall being at least 2.5 timesthe average thickness of the container sidewall.
 53. The preform ofclaim 49, the preform sidewall thickness varying from 0.074-0.120 inchand the container sidewall thickness ranging from 0.0250.032 inch. 54.The preform of claim 49, the average radial stretch ratio to produce thecontainer being less than approximately 4.5:1.
 55. The preform of claim49, the average radial stretch ratio to produce the container beingbetween approximately 1.5:1 and 4.5:1.
 56. The preform of claim 49, thepreform comprising at least 90% polypropylene.
 57. An injection moldedpreform for stretch blow molding a container comprising polypropylene,the preform defining a longitudinal axis and comprising a finish havinga support flange, and a preform blow section comprising a neck extendingfrom the support flange, a sidewall extending from the neck and a baseclosing the blow section, the base having a portion of increasedthickness defining a thickness greater than all other portions of theblow section, a lower end of the sidewall and the base are directedinward toward the preform longitudinal axis.
 58. The preform of claim57, the base portion thinning from the base portion of increasedthickness to the preform longitudinal axis.
 59. The preform of claim 57,the sidewall increasing in thickness from the neck to the base.
 60. Thepreform of claim 57, comprising an intermediate barrier layer.
 61. Thepreform of claim 57, the preform comprising at least 90% polypropylene.62. An injection molded preform for stretch blow molding a containercomprising polypropylene, and having a finish, a neck extending from thefinish, a sidewall extending from the neck and a base extending from thesidewall, the preform comprising a finish having a support flange, and apreform blow section having a neck extending from the support flange, asidewall extending from the neck and a base closing the blow section,the preform facilitating an average radial stretch ratio of less thanapproximately 4.5:1 to produce the container.
 63. The preform of claim62, the average radial stretch ratio to produce the container beingbetween approximately 1.5:1 and 4.5:1.
 64. The preform of claim 62, thepreform comprising at least 90% polypropylene.
 65. The preform of claim62, the axial stretch ratio to produce the container being less thanapproximately 1.6:1.